The objective of this project is to continue development of a prototype silt scan flow cytometer capable of processing one thousand chromosomes per second for karyotyping and aberration detection. In this instrument, fluorescently stained metaphase chromosomes will flow lengthwise through a narrow ribbon of exciting laser light. The emitted fluorescence will be measured and will provide a time dependent signal profile corresponding to the stain content along the length of the chromosome. The profile will be recorded and used to determine the chromosome stain content and centromeric location and number. In the coming year, we will a) modify the slit-scan system to allow ultraviolet excitation of chromosomes stained with the highly DNA specific dye 33258 Hoechst, b) develop computer programs for chromosome classification from slit-scan profiles and c) compare the slit-scan measurements of centromeric index and DNA content with similar measurements made by scanning cytophotometry.